Most men assume they will be able to conceive a child with no difficulty. However, 10-20% of all couples attempting pregnancy are infertile, with male factor infertility accounting for 40-50% of the cases. For most male infertility cases, the etiology is unknown and specific therapy is not available. Diagnosis of infertility can be a distressing life crisis, and the absence of a clear understanding of the pathophysiology of the disease and the corresponding lack of efficacious treatment for most male-factor infertility underscores the need for novel approaches to better understand this condition. This proposal seeks to improve the understanding of the pathophysiology of male factor infertility and the ability to diagnose male infertility by investigating the epigenetic state of human spermatozoa and defining its physiologic role in male infertility. Epigenetic programming (altering heritable biological information without changing DNA nucleotide sequence) is a normal process that leads to modifications of gene activity that can be transmitted to daughter cells. Extensive epigenetic reprogramming occurs during normal maturation of germ cells and spermatogenesis. However, improper epigenetic programming can have adverse health effects. Our preliminary data indicate that levels of one epigenetic indicator, DNA methylation, are elevated in spermatozoa of men who have abnormal sperm numbers, motility and morphology. This pattern may be expected if disrupted epigenetic programming predisposes to male infertility. This is particularly intriguing in light of preliminary animal studies suggesting that toxic exposures that negatively affect semen parameters also alter sperm DNA methylation. We propose that assessment of DNA methylation profiles in the male germ line provides the opportunity to better understand the physiologic mechanisms leading to idiopathic male infertility and to develop sensitive biomarkers of disrupted epigenetic programming. We anticipate that these markers will provide a mechanistic explanation for a category of idiopathic infertility and improve the diagnosis of and ultimately the treatment of male infertility by allowing us to study the epigenetic state of the germ cell and its relationship to fertility outcomes. This project should improve our ability to diagnose male factor infertility by identifying an epigenetic role in the pathogenesis of male factor infertility and lead to the development of a biomarker of abnormal sperm function that can be used as 1) a screening test for male factor infertility;2) a predictor of fertility outcomes in an ART setting, and 3) a marker/predictor of adverse fertility outcomes following toxic exposures.